1. Field of the Invention
The present invention relates to an apparatus for reading from and/or writing to optical recording media which has a disk type identification means for identifying the type of recording medium, and also to a corresponding method.
2. Prior art
An apparatus of this type is disclosed in U.S. Pat. No. 5,414,684. In the case of this known apparatus, in order to identify the type of recording medium first of all an attempt is made to read the list of contents thereof, the so-called TOC or Table of Contents. If it is not possible to read the TOC, then one or a number of renewed attempts are made to read information at one or a number of other locations on the recording medium. The type of optical recording medium is inferred from the success or lack of success of these attempts.
What is disadvantageous about the known apparatus is that a complete set-up operation has to be performed for each attempt to read information. This operation includes, inter alia, the closing of focus regulating circuit, track regulating circuit, drive regulating circuit and the like. This procedure is relatively complicated and time-consuming.
An object of the invention is to propose an apparatus having disk type identification means which is able to reliably identify the type of the recording medium inserted into the apparatus within a short-time. A further object of the invention is to specify a corresponding method.
According to the invention, these objects are achieved by means of the features specified in the independent claims. Advantageous developments thereof are specified in the dependent claims.
According to the invention, the disk type identification means has a mirror signal detector, a threshold value generator, a counter and an evaluation unit. This has the advantage that rapid identification of the type of recording medium is attained. The disk type identification means has elements with a relatively simple function which enable information about the type of disk to be obtained even when the recording medium cannot yet be read even though the focus regulating circuit is closed. The mirror signal is a signal which assumes different values if the scanning means is scanning an information track or a region between two information tracks. In this case, the region located between two information tracks may be free of information, but it may also itself carry information, for example control information or else information of a kind which corresponds to that of the information tracks.
According to the invention, an input of the mirror signal detector is connected to an output of the scanning means and a further input is connected to the threshold value generator, and the counter is connected to an output of the mirror signal detector and to an input of the evaluation unit. In the case of this advantageous combination of the individual elements, the threshold value generator specifies a threshold value for the formation of the mirror signal. The counter counts the occurrence of specific states of the mirror signal, for example the number of high or low states, corresponding transitions, zero crossings or the like. The evaluation unit evaluates the counter reading for the purpose of determining the type of recording medium.
An advantageous development of the invention provides for the apparatus to have a layer thickness identification means. This has the advantage that the layer thickness identification means supplies an additional criterion by means of which specific settings of the apparatus are suitably preselected in order further to accelerate the identification of the type of disk. In addition or as an alternative, the additional criterion also serves as a criterion for the identification of the type of disk, thereby accelerating the identification or increasing its reliability. The layer thickness identification means serves for determining the thickness of a protective layer which is superposed on an information-carrying layer of the recording medium.
A further variant of the invention provides for the apparatus to have a spacing identification means for determining the spacing of different layers of the recording medium from one another. This additional criterion also contributes to accelerating and/or to increasing the reliability of the identification of the type of disk. In this case, the various levels are advantageously two or more information layers. However, it is also likewise within the scope of the invention for the layers to be other layers which are present in the structure of the optical recording medium and can be detected.
The invention""s method for identifying the type of an optical recording medium has the following method steps: aa) focusing onto an information layer of the recording medium; bb) setting of a threshold value for the generation of a mirror signal; cc) counting of transitions of the mirror signal; dd) determination of the type of the recording medium using the count. This has the advantage that a tracking mode and signal identification, that is to say reading of the information stored on the recording medium, are not necessary, which enables the type of disk to be identified rapidly. As soon as the type of recording medium has been identified, apparatus settings which are adapted to this type of recording medium, in particular for focus, tracking and other regulating circuits, are selected. As a result, the start-up phase, that is to say the time from the insertion of the recording medium into the apparatus or from the issuing of a start command until the beginning of playback or recording, can be kept short. Consequently, the waiting time for the user is advantageously shortened.
According to the invention, in step dd), the recording medium is determined as being associated with an nth type if the count lies in an nth range of values, where n is an integer. This has the advantage that, if appropriate, a multiplicity of different types of recording media can be identified without the counts necessarily having to be exact. In the simplest case a check is made to see whether the count is greater or less than a limit value. This limit value is regarded as the limit between two ranges of values. In the extreme case, a single type of recording medium is identified for example by virtue of the fact that the count is greater than a limit value. For n=2, by way of example, the recording medium is determined as being associated with a first type if the count lies between zero and a first value m1, while it is determined as being associated with a second type if the count lies between a second value m2 and a third value m3. In this case, it is perfectly possible for the start value m0 also to be a value other than zero, or for the first value m1 and second value m2 to be identical. The same applies correspondingly to three or a larger number of disk types to be identified.
An advantageous development of the method provides for the scanning beam of the scanning means of the apparatus to be moved across a region of the recording medium which is larger than a region which corresponds to the maximum eccentricity that occurs. This had the advantage that more rapid and more reliable identification is made possible by the large number, achieved as a consequence, of information tracks crossed by the scanning beam. In this case, the eccentricity includes both the production-dictated eccentricity of the recording medium, that is to say the circular or spiral information tracks thereof which are not centred exactly with respect to the axis of rotational symmetry, and eccentricity engendered by operation, for example due to inexact centring of the recording medium in the apparatus. The eccentricity is subject to tolerance ranges which, in practice, are generally not exceeded and which serve here as a lower limit for the induced movement of the scanning beam.
An advantageous refinement of the invention provides for steps bb) to cc) to be performed a number of times, a different threshold value being set in each case in step bb). This has the advantage that a larger number of different types of disk can be identified relatively rapidly. A further advantage is that, in combination with a plurality of ranges of values, a small number of passes suffices to be able to distinguish a large number of different types. Furthermore, counterchecking by means of different passes makes it possible to increase the checking reliability relatively rapidly.
The invention furthermore provides, after the type of recording medium has been determined, for a check to be made to see whether focusing onto a further information layer is possible. This has the advantage that the presence of a multilayer recording medium is already effected with apparatus settings which are adapted to the recording medium, which reduces the time that elapses until complete identification of the disk type has ended, and also enables multilayer recording media to be identified.
According to a further refinement of the invention, the method according to the invention is first of all utilized for identifying the type of information layer onto which the optical scanning unit effects focusing, then the settings of the apparatus are adapted to the layer type that has been determined, information is read from the said information layer and the type of recording medium is determined from the information read. This method has the advantage that the identification operation is again shortened, since it is not necessary to search for further information layers if the presence and, if appropriate, the type of further layers can be identified from the information read from the first information layer.
A variant of the invention provides for the mirror signal detector of the apparatus to have at least one element which is variable as a function of frequency. This has the advantage that an element which is variable as a function of frequency can be adaptively matched in terms of its properties to the track crossing frequency during operation, with the result that interfering influences which occur in certain frequency ranges are compensated for or minimized in a frequency-selective manner. The mirror signal detector generates a mirror signal indicating whether the scanning means is scanning a data track or is located between two data tracks. To that end, the high-frequency signal read from the disk is considered, in general. It has a high degree of modulation if the scanning means is scanning a data track, whereas it is only weakly modulated if the scanning means is scanning between two data tracks. It is the case at high track crossing frequencies that the differences in modulation between data track and the interspace between two data tracks are only very small. Slightly modulated input signals occur for example in the case of high-density recording media. In that case, when an information track is traversed, the intensity of the high-frequency signal decreases, in some instances, only by 20% in comparison with the traversal of the reflective region lying between the information tracks, whereas this value is approximately 65% in the case of conventional compact discs. The apparatus advantageously has a control device which influences the threshold value-forming unit and also a track regulator. This has the advantage that in order to determine the type of optical recording medium, the track regulator is inactivated and the threshold value-forming unit is set to a fixed threshold value. The effect of switching off the track regulator is that information tracks of the recording medium are traversed. Depending on the type of recording medium, it is possible to establish a mirror signal with regard to a suitably set threshold value or this is not possible, and from this a conclusion is drawn regarding the type of optical recording medium. The averaging is likewise effected as a function of the frequency of the mirror signal. This has the advantage that in the event of a higher-frequency signal, the average value is also formed at a higher frequency in order to be matched as quickly as possible to a possibly altered signal intensity, as occurs e.g. in the case of recording media having a high storage density, as specified above.
Furthermore, provision is made for an upper and a lower threshold value to be used instead of a single threshold value, the mirror signal being set to a first value, for example the value 1, when the upper threshold value is exceeded, and being set to a second value, for example the value 0 when the lower threshold value is undershot, its value otherwise being maintained. This has the advantage that the value of the mirror signal does not fluctuate to an unnecessarily great extent in the transition region between the two values, i.e. becomes smoother. The hysteresis prevents the value of the mirror signal from jumping back and forth in the transition region between the two values. As a result, the frequency determination of the mirror signal also becomes even more accurate and the quality of the method according to the invention is increased.
An advantageous variant of the method according to the invention consists in specifying a certain threshold value and in checking whether or not a mirror signal can be established with regard thereto. This has the advantage that the type of recording medium can be determined by means of a mirror signal detector which is present in any case, i.e. without any additional outlay. If a mirror signal can be established, then a first type of recording medium is being scanned; if, on the other hand, a mirror signal cannot be established, then a second type of recording medium is involved. The different types of recording media differ, for example, in terms of their track arrangement, the size of the track width or of the track spacing, as is the case for example with conventional CDs and recording media having a high storage density, such as DVDs.
In an advantageous manner a plurality of different threshold values are tested one after the other. This has the advantage of increasing the number of different types of recording media that can be identified. Consequently, types which vary only slightly in terms of their properties can also be distinguished using the mirror signal which can be determined with regard to different threshold values. For example, write-once, write-many and non-writable optical recording media differ, in some instances, only slightly with regard to the threshold value which is suitable for forming the mirror signal, yet they can be identified reliably by means of the method according to the invention on the basis of the plurality of threshold values used. The invention is suitable for distinguishing different types of recording media from one another, such as, inter alia, CD, CD-R, CD-RW and DVD, DVD-RAM and others.
According to the invention, information tracks of the recording medium are traversed during the implementation of the method steps, this being effected in the simplest case by switching off a track regulator and utilizing eccentricity of the recording medium or its mounting in the apparatus. It is particularly advantageous to actively implement traversal of information tracks. This has the advantage that the conditions for generating a mirror signal are always met and, consequently, even an absent mirror signal can be ascribed unambiguously to the type of recording medium.